INFICON Explorer Portable Gas Chromatograph - Manual (Page 319)

Explorer Operator Manual
317
It is impossible to completely eliminate integrator effects as a source of error over
the broad range of conditions under which
Explorer must operate. For this reason,
it is essential that you verify the integration results generated by the instrument by
examining the chromatograms and re-integrating, if necessary. This is particularly
true if the results are being used to make decisions regarding health and safety
issues.
Sampling Errors
Sampling errors occur when the concentration of a compound in the gas sample
presented to the analytical system is not the same as the original sample.
For example: A Tedlar bag is filled with styrene and sampled at regular intervals.
A graph of measured concentration versus time produces a curve as shown in
Figure 29. This measurement sequence lasted for about 8 hours. The last run was
performed approximately 8 hours after the initial sequence of runs had been
completed. This data trend is symptomatic of adsorption of styrene by the gas bag.
If the same concentration of styrene is measured directly from a tank of compressed
gas, standard drift effects over the same time period are negligible. If a Tedlar bag is
used to store a styrene sample at this concentration, then the analysis results hours
later will not accurately reflect the concentration at the time of sampling.
Sampled 8
hours after
end of
analysis
sequence
0.5
0.6
0.7
0.8
0.9
1
0 5 10 15 20
Hours
Figure 29 Gas Bag Effect as Measured on a 1 ppm Styrene Sample